The present invention relates to a cartridge valve for installation in a manifold having a receiving cavity.
Cartridge valves are widely used for proportionately and/or precisely controlling fluid flow or pressure through passages of a hydraulic circuit. In its simplest form, a cartridge valve is used in a receiving cavity of a manifold to regulate the flow of fluid from an inlet port to an outlet port communicating with the receiving cavity. Such cartridge valves are used to controllably operate a fluid circuit and to precisely set and maintain a desired flow through the passage.
Prior art cartridge valves encounter a problem because the design of the valves require precise forming of the receiving cavity in the manifold. If the receiving cavity is not precisely formed in accordance with the required tolerances of the prior art cartridge valve a cage portion of the valve tends to bind or cant against the receiving cavity walls. When the valve binds, a spool portion retained in the cage portion does not freely operate. When the spool does not freely operate, the circuit does not perform as originally designed and additional steps must be taken to determine why the circuit is not operated.
Often times, the cartridge valve is removed and assumed to be defective whereupon a different cartridge valve is installed in the receiving cavity. After a number of attempts with alternate cartridge valves, the mechanic diagnosing the problem may determine that the receiving cavity is the problematic area. The receiving cavity may have to be reworked in order to accommodate the cartridge valve. It should be noted, however, that reworking a receiving cavity may also create problems in that the cavity may become oversized and thereby not providing proper seating and sealing of the cartridge valve installed therein.
Clearly, the problems inherent in prior art cartridge valves require substantial time, effort, and cost. These problems may be escerbated when a valve, which is properly working, fails to operate due to a change in operating conditions. Cartridge valves are used in an environment which is prone to thermal expansion and contraction. Additionally, particulate matter carried in the fluid flow may build up in the valve and foul its operation. With regard to thermal variations, temperature increases may cause the manifold material to expand thereby changing the tolerance of what was previously an acceptable valve. Cooling of the manifold material may provide a similar tolerance variation problem. When the valve tolerances change as a result of thermal expansion or contraction, the valve may bind or leak.
Another problem with prior art cartridge valves occurs as a result of a sampling valve formed in the spool becoming clogged with particulate matter which may be carried in the fluid flow. Since the manifolds are often constructed of metallic materials, particles may be left in the passages and cavities from the original casting and/or machining operations of the manifold. Such particles are carried in the fluid flow once the system is charged. Additionally, particles remaining from the original manufacturing process of the manifold may cause additional wear and thus produce additional particulate matter. When particulate matter is delivered to the spool of a cartridge valve, the sampling orifice may become clogged with such particulate matter. Cleaning of the spool requires extraction of the cartridge valve from the receiving cavity. Removal of the cartridge valve involves depressurizing and draining at least the specific lines associated with the receiving cavity. The removal and cleaning operations require substantial time, effort, cost as well as downtime and the associated downtime costs.
Yet an additional problem found in prior art cartridge valve is that the handle or knob assemblies used to operate and adjust the valves are prone to separation from the cartridge valve. Prior art knob assemblies are attached to the cartridge valve by means of a threaded fastener extending through an adjusting screw portion of the cartridge valve. If the fluid pressure on the adjusting screw is great enough, substantial force may have to be applied through the screw to break open the valve. However, if the force required to brake the valve open is greater than the strength of the material in the screw, or the threaded connection, the fastener may torque off or the threads between the fastener and the adjusting screw may be stripped. Additionally, if the adjusting screw is operated into a maximum limit of the adjusting range, continued application of force to the knob assembly may result in the similar damage. If a knob assembly is damaged, replacement or repair of the knob assembly and associated cartridge valve may require substantial time, effort, cost and associated downtime and cost.
The problems associated with damaged knob assemblies are further escerbated when the failure of the knob assembly causes damage to the control valve. Damage to the control valve may result while boring out a stripped threaded fastener and forming new threads therein. If the adjusting screw is overdrilled during the boring operation, the valve may leak and become irreparably damaged. The additional boring of the adjusting screw also may reduce the strength of the adjusting screw thereby creating a potential fatigue point in the adjusting screw itself. The fatigue point may be the place where the knob assembly fails the next time it is overtorqued.
As it can be seen, there are numerous problems with prior art cartridge valves and knob assemblies. The invention as shown and described herein satisfies the requirements for overcoming the above-described problems.